How Many GPS's

[bendyone]

How Many GPS\'s

Hi

Given the low cost of basic GPS hpow many should I carry. fixed or handheld.
One for the VHF DSC, one for the repeater outside / nav station, and one for the laptop chartplotter?

Can you get carried away by safty concerns and equipment that might go wrong?

 

[Anonymous]

Re: How Many GPS\'s

Can you get carried away? Don't know, but as the cost of the GPS engine falls why not put them where you need them and not try to connect them by wires? I have 3 GPS EPIRBS (1 main, 1 personal locator and 1 in liferaft), 1 main GPS, 1 GPS purely for the DSC VHF, 1 standalone plotter with integral GPS (just plugs into 12V cigar lighter wherever we want it - in our cabin, on deck...) and one old basic handheld which we use in the car, tender, or whatever. That's six GPSs.

What do you do if you only have two and they disagree? Revert to traditional methods?

 

[lockwood]

Re: How Many GPS\'s

I would imagine that just one GPS chartplotter with an nmea link to a dsc set would be enough for anyone.

Maybe a small handheld unit in a liferaft for those with bigger boats. Oh, yes, and a EPRIB gps unit.

OK, I get your point!

 

[Piers]

Re: How Many GPSs?

Aha. I think you are questioning that if the one you carry starts to go wrong, how do you know?

If you have 2, it could be tricky to tell which of the two has started to go AWOL.

If you had 3, the one in error will always stand out against the other two.

Having said that, ever since GPS started, I've never had one go wrong. What I have found is that when loading each one separately (the best way so common errors are not made) I have made errors when loading waypoints. When one starts going off track, it is a much easier task to find where the error lies.

Finally, you ask whether fixed or hand held. I use a fixed for the chart plotter, DSC, radar and autopilot, with a hand held backup always plotting the same course. This can always be grabbed for a liferaft situation. I also have another basic fixed as the third.

Some say overkill....some have more! Mine works for me.

Note also that most GPSs plot tracks using great circles. However, one or two are starting to use rhumb lines. Hence, ensure you know which your GPSs use in case they are different and thereby start to show you going off track.

Most boating charts we use are Mercator charts. On these, joining waypoints creates a rhumb line. If your GPS is plotting a great circle route, you will start and end at the right points, but during the tracking, the great circle GPS will take you north of the rhumb line in the Northern hemisphere. These differences are zero if travelling due north / south, and worst when travelling due east / west.

From memory, if using a great circle GPS, a 50nm east west route in our latitudes will show a track some 200m to the north of a rhumb line track drawn on a Mercator chart at its mid point.

If you don’t know whether your navigator calculates great circle or rhumb line tracks, check the manual, or contact the manufacturer’s representative. Failing that, plot a long east/west leg of at least 100nm, preferably more and see if the course to steer is shown as north of the expected 090°T or 270°T.

 

[BobOwen]

Re: How Many GPS\'s

"What do you do if you only have two and they disagree? Revert to traditional methods?"

Reverting to traditional methods is of course, the only possibility. What do you do if GPS is off? A chart, plotter and MK1 eyeball is a better back up than another dozen GPS's. Whats needed is an alternative backup, not more of the same surely?.

I can imagine how you have arrived at seven (Not six) seperate GPS systems and imagine each is justified at the time of purchase. It does sound pretty incredible though. Thats more than an ocean going tanker or a 747 probably has isn't it?
So many, you're not exactly sure how many you have! /forums/images/graemlins/smile.gif

Two gps's on board sounds like a reasonable number considering the cost and but four navigational systems is overkill IMHO. (Discounting the epirbs)
If it really does increase safety, it follows that ten GPS's on board will make you very safe........

 

[jerryat]

Re: How Many GPS\'s

Oh Dear! Makes me feel I've gone a bit OTT then. We have a fixed Phillips GPS (fabulous) and three handheld, waterproof back-ups. One lives in the grab/panic container together with lots of spare batteries, and the other two are there to make us feel comfy! I got my Yachtmaster quals. back in '79 and most of my occasional crew for for the longer passages are similarly experienced, so a total gps 'downer' wouldn't faze us at all. We used a sextant for the fun of it all the way on our last Atlantic circuit and got really accurate results - checked against the GPS.

However, used sensibly (i.e. not totally depended on) I do think GPS increases sailing pleasure and safety. Like many others, I was taught to keep an accurate, hourly, log in the days long before Decca, and this is still done aboard my boat, EVEN on the 'Pond' circuits where, strictly speaking I suppose, 6 hourly ones would have sufficed.

But then, we had lots of time each day ................

Ok, I'm a bit old-fashioned and have absolutely nothing 'inter-faced' with anything else. If anything goes wrong with a piece of kit, I want the 'chain' to stop there!

Cheers
Jerry

 

[duncan]

Re: How Many GPS\'s

2

One fixed and linked to the other fixed items; one handheld, waterproof and battery powered. This will of course match your VHF setup.
If you loose boat power (for any reason) or have to abandon ship (for any reason) you retain position and communication capabilities (however limited the latter!).

 

[Anonymous]

Re: How Many GPS\'s

[ QUOTE ]
Two gps's on board sounds like a reasonable number considering the cost and but four navigational systems is overkill IMHO. (Discounting the epirbs)
If it really does increase safety, it follows that ten GPS's on board will make you very safe........

[/ QUOTE ]No, it has nothing to do with safety. It is easier to put these things where the function is needed than it is to bus everything together. There is an advantage, too, in that if a bus goes down then so does everything connected to it so it should be marginally more reliable, at least in theory. These days active outdoor types tend to have handheld GPSs so you could well find that everyone on board has their own personal GPS!

Having said that, if someone is so nervous about losing the GPS service that they feel it necessary to provide multiple redundancy, in most cruising territories I would be wondering whether they had sufficient knowledge or experience of traditional methods; after all, the GPS service could, itself, be witheld on the outbreak of hostilities, technical failure or military interference.

David

 

[MapisM]

most GPSs plot tracks using great circles

I thought to have seen quite some plotters (Simrad, Furuno, Raymarine, B&O and Garmin - unless I'm forgetting others).
Never saw great circles routes on them, I've just found the functionality it on a PC-based navigation SW.
Which models are you talking about?

 

[john_morris_uk]

Re: most GPSs plot tracks using great circles

Most if not all GPS receivers do plot routes on a great circle basis. For the average user in coastal waters, you will never notice the difference as some-one else has pointed out.

/forums/images/graemlins/blush.gif Should I feel utterly inadequate? We have 'one' yes 'only one' GPS on the boat. Its a fixed one at the chart table that not only outputs to the DSC radio but we have a ST60 graphics display in the cockpit to tell us what it says from on deck. I don't have a hand-held - never got round to buying one...

 

[Shantyman]

Re: How Many GPSs?

Piers said:
"If you have 2, it could be tricky to tell which of the two has started to go AWOL. . . ."

I think you would have to examine both sets very carefully and see which one had sprouted the legs or wings without which it would be difficult to go AWOL (Absent WithOut Leave).

Cheers

 

[Colvic Watson]

Re: How Many GPS\'s

Seven GPS sets?! For goodness sake. Why not three engines; four life rafts (they are notoriously unreliable) and five VHF radios (plus a spare boat).

I blame PBO; all those scare stories........

 

[muchy_]

Re: How Many GPS\'s

I have two. One fixed and wired to DSC and one handheld with battery backup.

 

[Koeketiene]

Re: How Many GPS\'s

Have got one fixed GPS always on - linked to radar, Navtex, autopilot & repeater by the wheel.
Have one chartplotter with it's own antenna for use in fog & at night.

Have one handheld GPS in case everything goes wrong.

 

[duncan]

Re: How Many GPS\'s

[ QUOTE ]
Have one handheld GPS in case everything goes wrong

[/ QUOTE ]

bottle of rum does us for that............ /forums/images/graemlins/cool.gif

 

[Thistle]

Re: How Many GPS\'s

[ QUOTE ]
Have got one fixed GPS always on - linked to radar, Navtex, autopilot & repeater by the wheel.
Have one chartplotter with it's own antenna for use in fog & at night.

[/ QUOTE ]

... and some folk - perhaps not you, Yanita - criticise PBO for concentrating on safety issues. Isn't it we sailors who are fixated on navigational aids which we happily keep on adding to - multiple GPS sets - to give us greater safety (or at least an illusion of greater safety)?

 

[Koeketiene]

Re: How Many GPS\'s

I do admit being on the cautious side.
Reasons for this:
1. Yanita's a family boat - crew's wife (not a keen sailor due to bouts of seasickness), 14 yr old daughter & 9 yr old son. When it starts blowing, it's me & me alone: helming (once over F5 autopilot can not cope), setting the sails, reefing & nav. At that time I have neither the time or inclination to work out CTS, EP or do 3 point fixes.
2. Lesson learned in naval life: redundancy.
3. And how's this for belt & braces? Also carry sextant & set of tables

 

[Jack_the_Lad]

Re: How Many GPS\'s

Get yourself a sextant and learn how to use it !

When the US turn off the Sats you're not lost - learn to navigate properly.
All this electric stuff bah, humbug ;-)

 

[Guest]

Re: most GPSs plot tracks using great circles

I would suggest that it is actually Spherical Trig and not great circle ....

Unless you are crossing the oceans - it makes gnats difference to the average yottie. /forums/images/graemlins/wink.gif

 

[Piers]

Re: most GPSs plot tracks using great circles

I suspect you'll find almost all use GCs. Use the test I mentioned above to check yours. It is very rare to find one that does Rhumb Lines.

The reason for mentioning GC versus RL is that when we are led to believe GPS accuracy 10m or less, we need to be aware that the error caused by using a GC GPS to naivigate when you've plotted a RL route on your Mercator paper chart, we can introduce errors of much greater magnitude.

When I'm cruising along the South Coast, it's fun seeing the Garmin Hand Held want to take me north of track when my Simradr (set to RL) keeps me where the paper chart wants me!